This invention relates to a rotor for a flywheel magneto generator having a reluctor provided thereon.
A flywheel magneto generator has been used as a generator mounted on an engine. The flywheel magneto generator comprises a rotor mounted on a crankshaft of the engine and a stator secured to an engine case, for example. The rotor of the magneto generator comprises a cup shaped flywheel having a peripheral wall portion and a bottom wall portion provided so as to close one end of the peripheral wall portion as viewed in an axial direction and permanent magnets mounted on an inner face of the peripheral wall portion of the flywheel. A boss provided at a central portion of the bottom wall portion of the flywheel is secured to the crankshaft.
There is required information about a crank angle and a rotational speed for controlling the ignition timing of the engine and controlling the injection of the fuel. An inductor type signal generator is used for obtaining the information. The signal generator comprises a signal generating rotor having a signal generating reluctor (an inductor) of projection provided on an outer face thereof and rotated in synchronization with the engine and a stator called as a pulser. The pulser comprises an iron core having a magnetic pole portion to be faced with the reluctor, a pulser coil wound on the iron core and a permanent magnet magnetically connected with the iron core. A pulse signal is generated from the pulser coil when the reluctor begins being faced with the magnetic pole portion of the iron core of the pulser as the crankshaft of the engine rotates and when the reluctor finishes being faced with the magnetic pole portion of the iron core.
In many cases where a flywheel magneto generator is used as a generator mounted on the engine, the flywheel is used as the rotor of the pulser by providing the signal generating reluctor on an outer face of the peripheral wall portion of the flywheel.
The flywheel to be used as the rotor of the flywheel magneto generator is produced either by a press process or by a casting process or a thermally forging process.
FIGS. 7A and 7B show the rotor for the magneto generator having the flywheel produced by the press process. The flywheel 1 comprises a cylindrical peripheral wall portion 1a and a bottom wall portion 1b provided so as to close one end of the peripheral wall portion 1a as viewed in an axial direction of the flywheel 1. A boss 1c formed separately from the flywheel 1 is secured to a central portion of the bottom wall portion 1b by rivets, for example. A reluctor 2 is formed on the peripheral wall portion 1a of the flywheel 1 by embossing a portion of the peripheral wall portion 1a in a radial direction by the press processing. Permanent magnets 4 are attached onto an inner face of the peripheral wall portion 1a of the flywheel 1.
As the flywheel is produced by the press process in this manner, the reluctor 2 is formed by the press process after the flywheel 1 is produced and therefore a hollow portion 3 having a size mostly corresponding to that of the reluctor 2 is formed inside of the reluctor 2. FIGS. 8A, 8B, 9A, 9B and 10 show various rotors using the flywheel 1 produced by the casting process or the thermally forging process. In these rotors, the boss 1c is formed integrally with the bottom wall portion 1b of the flywheel 1. The reluctor 2 is formed on the outer face of the peripheral wall portion 1a of the flywheel 1 without forming any hollow portion inside of the reluctor 2.
Since the hollow portion 3 having the size mostly corresponding to that of the reluctor 2 is formed inside of the reluctor 2 in the case where the flywheel 1 is produced by the press process as shown in FIGS. 7A and 7B, troublesome breakdown of static balance of the flywheel 1 that tends to be caused by the presence of the reluctor 2 does not arise.
On the other hand, since no hollow portion is formed inside of the reluctor 2 in the case where the flywheel is produced either by the casting process or by the thermally forging process as shown in FIGS. 8A, 8B, 9A, 9B and 10, the breakdown of the static balance of the flywheel 1 that cannot be disregarded arises. Thus, as the static unbalance of the flywheel 1 that cannot be neglected arises due to the present of the reluctor in this manner, it is required to have the static balance of the flywheel 1 by providing static unbalance correction means such as a hole, a recess or a projection formed in the portion of the flywheel in order to correct the static unbalance of the flywheel.
When the static unbalance correction means is formed of the hole or the recess, it is provided closer to the reluctor relative to the center axis of the flywheel. In the case where the static unbalance correction means is formed of the projection, it is provided close to the side opposite to the reluctor relative to the boss of the flywheel.
The static unbalance correction means should be provided at a position where it is shifted in an axial direction of the flywheel relative to the reluctor so that it does not become an obstacle of the permanent magnets provided on the inner face of the flywheel and does not adversely affect the pulser.
In the example of FIGS. 8A and 8B, the static balance of the flywheel is maintained by the static unbalance correction means 5A of an extension hole provided in the bottom wall portion 1b of the flywheel 1 at a position adjacent to the reluctor 2.
In the example of FIGS. 9A and 9B, the static balance of the flywheel is maintained by the static unbalance correction means 5B of the projection provided on the inside of the bottom wall portion 1b of the flywheel 1 at a position opposite to the reluctor 2 relative to the boss portion 1c of the flywheel 1.
In the example of FIG. 10, the static balance of the flywheel is maintained by the static unbalance correction means 5C of the recess provided in the outer face of the bottom wall portion 1b of the flywheel 1 at a position adjacent to the reluctor 2.
As aforementioned, in the case where the static balance breaks due to the provision of the reluctor on the flywheel, the static unbalance correction means is provided in the state where it is shifted in the axial direction of the flywheel relative to the reluctor. However, if the static unbalance correction means is shifted in the axial direction of the flywheel relative to the reluctor as aforementioned, then there occurs the problem that the dynamic balance of the flywheel breaks. Particularly, as the width of the reluctor gets larger and the mass of the reluctor gets larger, the breakdown of the dynamic balance cannot get disregarded and the vibration of the rotor when the engine rotates at a high speed disadvantageously becomes larger. As the vibration of the rotor when the engine rotates at the high speed becomes larger, the waveform of the output of the pulser is possibly distorted or a noise possibly arises from the pulser due to variation in an air gap between the reluctor and a not shown magnetic pole portion of the pulser.
Accordingly, it is a principal object of the invention to provide a rotor of a flywheel magneto generator adapted to correct a breakdown of dynamic balance caused by static unbalance correction means.
The invention is applied to a flywheel magneto generator comprising a flywheel having a peripheral wall portion and a bottom wall portion to close one end of the peripheral wall portion as viewed in an axial direction with a reluctor of projection provided on an outer face of the peripheral wall portion and permanent magnets provided on an inner face of the peripheral wall portion of the flywheel, wherein static unbalance correction means to correct static unbalance of the flywheel caused by the presence of the reluctor is provided on the flywheel at a position where it is shifted to one side of the flywheel as viewed in an axial direction thereof relative to a center of the reluctor. In the present invention, the flywheel further comprises dynamic unbalance correction means to correct dynamic unbalance of the flywheel caused by the static unbalance correction means and the reluctor. The dynamic unbalance correction means is provided at a position where it is shifted to the other side of the flywheel relative to the reluctor as viewed in the axial direction.
In the case where the static unbalance correction means is provided on the bottom wall portion of the flywheel at the position where it is closer to the reluctor, a recess or recesses for the dynamic unbalance correction means may be preferably formed in an end face of the bottom wall portion on the other side in the axial direction at the position closer to the reluctor.
The dynamic unbalance correction means may be preferably provided so that the composite moment of the static balance moment of the static unbalance correction means and the static balance moment of the dynamic unbalance correction means is balanced with the static balance moment of the reluctor.
With the dynamic unbalance correction means provided as aforementioned, the breakdown of the dynamic balance caused by the provision of the static unbalance correction means can be corrected so as to maintain the dynamic balance of the flywheel, whereby the troublesome vibration of the rotor when the engine rotates at the high speed can be prevented.